Organic thin film transistor

ABSTRACT

An organic thin film transistor includes a substrate, a source/drain layer that is located on the substrate and has a source region and a drain region, a first buffer layer that is located between the source region and the drain region, a semiconductor layer that is located on the source/drain layer and the first buffer layer, a gate insulating layer, and a gate electrode. The first buffer layer covers at least one portion of the source region and at least one portion of the drain region. The first buffer layer is located among the semiconductor layer, the source region, the drain region, and the substrate. The gate insulating layer covers the source/drain layer and the semiconductor layer. The gate electrode is located on the gate insulating layer, and a portion of the gate insulating layer is located between the gate electrode and the semiconductor layer.

RELATED APPLICATIONS

This application claims priority to China Application Serial Number201710324191.0, filed May 10, 2017, which is herein incorporated byreference.

BACKGROUND Field of Invention

The present invention relates to an organic thin film transistor.

Description of Related Art

Generally speaking, a source/drain layer of an organic thin filmtransistor is made of gold, silver, or another material that can reactwith a self-assembly monolayer (SAM), in which the self-assemblymonolayer is a semiconductor layer of the organic thin film transistor.

In manufacturing an organic thin film transistor, the source/drain layeris patterned to form a source region and a drain region that are spacedapart at a gap, and then a semiconductor layer is formed on the sourceregion and the drain region adjacent to the gap, and is formed in thegap between the source region and the drain region by coating. However,due to limitations of materials of the source region and the drainregion, after the source/drain layer is patterned, a taper undercutstructure is formed on the source region and the drain region that areadjacent to the gap. As a result, the semiconductor layer in the gap andadjacent to the taper undercut structure has a greater thickness, andthe semiconductor layer with the greater thickness will affect moleculararrangements. In other words, the semiconductor layer with non-uniformthickness will cause adverse effects on stability of electricalproperties of the organic thin film transistor.

SUMMARY

An aspect of the present invention is to provide an organic thin filmtransistor.

According to an embodiment of the present invention, an organic thinfilm transistor includes a substrate, a source/drain layer, a firstbuffer layer, a semiconductor layer, a gate insulating layer, and a gateelectrode. The source/drain layer is located on the substrate and has asource region and a drain region. The first buffer layer is locatedbetween the source region and the drain region, and covers at least oneportion of the source region and at least one portion of the drainregion. The semiconductor layer is located on the source/drain layer andthe first buffer layer. The first buffer layer is located among thesemiconductor layer, the source region, the drain region, and thesubstrate. The gate insulating layer covers the source/drain layer andthe semiconductor layer. The gate electrode is located on the gateinsulating layer, and a portion of the gate insulating layer is locatedbetween the gate electrode and the semiconductor layer.

In one embodiment of the present invention, the organic thin filmtransistor further includes a protective layer. The protective layer isdisposed along the semiconductor layer. The semiconductor layer islocated between the protective layer and the source/drain layer, and islocated between the protective layer and the first buffer layer.

In one embodiment of the present invention, the organic thin filmtransistor further includes a photoresist layer. The photoresist layeris located on the protective layer and is located between the gateinsulating layer and the protective layer.

In one embodiment of the present invention, the organic thin filmtransistor further includes a barrier layer. The barrier layer islocated on the substrate, and the first buffer layer is located amongthe semiconductor layer, the source region, the drain region, and thebarrier layer.

In one embodiment of the present invention, the organic thin filmtransistor further includes a second buffer layer. The second bufferlayer is located on the barrier layer, and the first buffer layer islocated among the semiconductor layer, the source region, the drainregion, and the second buffer layer.

In one embodiment of the present invention, the source region has afirst surface and a second surface opposite the first surface, and has asidewall adjacent to the first surface and the second surface, and thefirst surface faces the substrate, and an obtuse angle is formed betweenthe sidewall and the first surface.

In one embodiment of the present invention, the first buffer layer has acentral portion and an extending portion, and the central portion islocated between the source region and the drain region, and theextending portion is located on the second surface of the source region.

In one embodiment of the present invention, at least one portion of thesource region is located between the extending portion and the centralportion.

In one embodiment of the present invention, the first buffer layer is incontact with the sidewall of the source region.

In one embodiment of the present invention, the drain region has a firstsurface and a second surface opposite the first surface, and has asidewall adjacent to the first surface and the second surface, and thefirst surface faces the substrate, and an obtuse angle is formed betweenthe sidewall and the first surface.

In the aforementioned embodiments of the present invention, because thefirst buffer layer is located between the source region and the drainregion, and covers at least one portion of the source region and atleast one portion of the drain region, the semiconductor layer may belocated on the source/drain layer and the first buffer layer. In such aconfiguration, the first buffer layer may be utilized to fill a spacebetween the source region and the drain region, thereby preventing thesemiconductor layer from being formed on taper undercut structures ofthe source region and the drain region, thus preventing thesemiconductor layer from having a greater thickness. As a result, thesemiconductor layer has uniform thickness, and does not affect moleculararrangements, and thus stability of electrical properties of the organicthin film transistor can be improved.

It is to be understood that both the foregoing general description andthe following detailed description are by examples, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the followingdetailed description of the embodiments, with reference made to theaccompanying drawings as follows:

FIG. 1 is a cross-sectional view of an organic thin film transistoraccording to one embodiment of the present invention;

FIG. 2 is a cross-sectional view of an organic thin film transistoraccording to one embodiment of the present invention;

FIG. 3 is a cross-sectional view of an organic thin film transistoraccording to one embodiment of the present invention;

FIG. 4 is a cross-sectional view of an organic thin film transistoraccording to one embodiment of the present invention; and

FIG. 5 is a cross-sectional view of an organic thin film transistoraccording to one embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are used in thedrawings and the description to refer to the same or like parts.

FIG. 1 is a cross-sectional view of an organic thin film transistor 100according to one embodiment of the present invention. As shown in FIG.1, the organic thin film transistor 100 includes a substrate 110, asource/drain layer 120, a first buffer layer 130, a semiconductor layer140, a gate insulating layer 150, and a gate electrode 160. Thesource/drain layer 120 is located on a surface of the substrate 110. Thesource/drain layer 120 has a source region 122 and a drain region 124that are spaced apart from each other at a gap. The first buffer layer130 fills the gap. In other words, the first buffer layer 130 is locatedbetween the source region 122 and the drain region 124. Moreover, thefirst buffer layer 130 further extends onto the source region 122 andthe drain region 124, thereby covering at least one portion of thesource region 122 and at least one portion of the drain region 124. Theaforementioned first buffer layer 130 may be made of material includinghigh-molecular polymer.

The semiconductor layer 140 is located on the source/drain layer 120 andthe first buffer layer 130, and thus the first buffer layer 130 islocated among the semiconductor layer 140, the source region 122, thedrain region 124, and the substrate 110. Stated differently, the firstbuffer layer 130 is surrounded by the semiconductor layer 140, thesource region 122, the drain region 124, and the substrate 110. The gateinsulating layer 150 covers the source/drain layer 120 and thesemiconductor layer 140. The gate electrode 160 is located on the gateinsulating layer 150, and a portion of the gate insulating layer 150 islocated between the gate electrode 160 and the semiconductor layer 140.

In this embodiment, the source/drain layer 120 may be made of a materialincluding silver or gold. When the source/drain layer 120 is patterned(e.g., by an etching process), taper undercut structures are formed onthe source region 122 and the drain region 124, thus forming obtuseangles θ1 and θ2. In addition, the gate insulating layer 150 may be madeof an organic material to act as an organic gate insulator (OGI).

The semiconductor layer 140 may be formed by spin coating or slitcoating, but the present invention is not limited in this regard. Sincethe first buffer layer 130 is located between the source region 122 andthe drain region 124, and covers at least one portion of the sourceregion 122 and at least one portion of the drain region 124, thesemiconductor layer 140 may be located on the source/drain layer 120 andthe first buffer layer 130. In such a configuration, the first bufferlayer 130 may be utilized to fill a space between the source region 122and the drain region 124, thereby preventing the semiconductor layer 140from being formed on areas of taper undercut structures of the sourceregion 122 and the drain region 124, thus preventing the semiconductorlayer 140 from having a greater thickness that causes the entiresemiconductor layer 140 to have non-uniform thickness and furtheraffects stability of electrical properties. Due to the first bufferlayer 130 under the semiconductor layer 140, the semiconductor layer 140may have uniform thickness in the formation of the semiconductor layer140, and thus stability of electrical properties of the organic thinfilm transistor 100 can be improved.

In this embodiments, the source region 122 has a first surface 125 a anda second surface 125 b opposite the first surface 125 a, and has asidewall 126 adjacent to the first surface 125 a and the second surface125 b. The drain region 124 has a first surface 127 a and a secondsurface 127 b opposite the first surface 127 a, and has a sidewall 128adjacent to the first surface 127 a and the second surface 127 b. Thefirst surface 125 a of the source region 122 and the first surface 127 aof the drain region 124 face the substrate 110, and the second surface125 b of the source region 122 and the second surface 127 b of the drainregion 124 face away from the substrate 110. The obtuse angle θ1 isformed between the sidewall 126 and the first surface 125 a of thesource region 122, and the obtuse angle θ2 is formed between thesidewall 128 and the first surface 127 a of the drain region 124.

Furthermore, the first buffer layer 130 has a central portion 132 andextending portions 134 and 136, and the central portion 132 is locatedbetween the source region 122 and the drain region 124. The extendingportion 134 is located on the second surface 125 b of the source region122, and the extending portion 136 is located on the second surface 127b of the drain region 124. In addition, the first buffer layer 130 is incontact with the sidewall 126 and the second surface 125 b of the sourceregion 122, and is in contact with the sidewall 128 and the secondsurface 127 b of the drain region 124. As a result, at least one portionof the source region 122 is located between the extending portion 134and the central portion 132, and at least one portion of the drainregion 124 is located between the extending portion 136 and the centralportion 132. Such a configuration can ensure that the semiconductorlayer 140 near the sidewalls 126 and 128 (the taper undercut structures)is separated from the sidewalls 126 and 128 by the first buffer layer130, and is supported by the first buffer layer 130, thereby preventingthe semiconductor layer 140 from falling into a space between the sourceregion 122 and the drain region 124 and having non-uniform thickness.

It is to be noted that the connection relationships, materials, andadvantages of the elements described above will not be repeatedhereinafter, and other types of organic thin film transistors will bedescribed.

FIG. 2 is a cross-sectional view of an organic thin film transistor 100a according to one embodiment of the present invention. The organic thinfilm transistor 100 a includes the substrate 110, the source/drain layer120, the first buffer layer 130, the semiconductor layer 140, the gateinsulating layer 150, and the gate electrode 160. The difference betweenthis embodiment and the embodiment shown in FIG. 1 is that the organicthin film transistor 100 a further includes a protective layer 170, aphotoresist layer 180, and a barrier layer 190. The protective layer 170is disposed along a surface of the semiconductor layer 140. Thesemiconductor layer 140 is located between the protective layer 170 andthe source/drain layer 120, and is located between the protective layer170 and the first buffer layer 130.

Moreover, the photoresist layer 180 is located on the protective layer170, and is located between the gate insulating layer 150 and theprotective layer 170. The barrier layer 190 is located on the substrate110 and is disposed along a surface of the substrate 110, and thus thefirst buffer layer 130 of the organic thin film transistor 100 a islocated among the semiconductor layer 140, the source region 122, thedrain region 124, and the barrier layer 190. In other words, the firstbuffer layer 130 of the organic thin film transistor 100 a is surroundedby the semiconductor layer 140, the source region 122, the drain region124, and the barrier layer 190.

In this embodiment, the protective layer 170 may be made of an organicmaterial to act as an organic protective layer (OPL). The photoresistlayer 180 may be made of an organic material to act as an organicphotoresist (OPR). The barrier layer 190 may be made of a materialincluding silicon nitride (SiNx) or silicon oxide (SiOx), but thepresent invention is not limited in this regard.

FIG. 3 is a cross-sectional view of an organic thin film transistor 100b according to one embodiment of the present invention. The organic thinfilm transistor 100 b includes the substrate 110, the source/drain layer120, the first buffer layer 130, the semiconductor layer 140, the gateinsulating layer 150, the gate electrode 160, the protective layer 170,the photoresist layer 180, and the barrier layer 190. The differencebetween this embodiment and the embodiment shown in FIG. 2 is that theorganic thin film transistor 100 b further includes a passivation layer210 and a pixel electrode 220. The passivation layer 210 covers the gateelectrode 160 and the gate insulating layer 150, and the pixel electrode220 is located on the passivation layer 210. In this embodiment, thepassivation layer 210 may be made of an organic material to act as anorganic passivation (OPV) layer.

FIG. 4 is a cross-sectional view of an organic thin film transistor 100c according to one embodiment of the present invention. The organic thinfilm transistor 100 c includes the substrate 110, the source/drain layer120, the first buffer layer 130, the semiconductor layer 140, the gateinsulating layer 150, the gate electrode 160, the protective layer 170,the photoresist layer 180, and the barrier layer 190. The differencebetween this embodiment and the embodiment shown in FIG. 2 is that theorganic thin film transistor 100 c further includes a second bufferlayer 230. The second buffer layer 230 is located on the barrier layer190, and thus the first buffer layer 130 is located among thesemiconductor layer 140, the source region 122, the drain region 124,and the second buffer layer 230. In other words, the first buffer layer130 is surrounded by the semiconductor layer 140, the source region 122,the drain region 124, and the second buffer layer 230.

FIG. 5 is a cross-sectional view of an organic thin film transistor 100d according to one embodiment of the present invention. The organic thinfilm transistor 100 d includes the substrate 110, the source/drain layer120, the first buffer layer 130, the semiconductor layer 140, the gateinsulating layer 150, the gate electrode 160, the protective layer 170,the photoresist layer 180, the barrier layer 190, and the second bufferlayer 230. The difference between this embodiment and the embodimentshown in FIG. 4 is that the organic thin film transistor 100 d furtherincludes the passivation layer 210 and the pixel electrode 220. Thepassivation layer 210 covers the gate electrode 160 and the gateinsulating layer 150, and the pixel electrode 220 is located on thepassivation layer 210.

Although the present invention has been described in considerable detailwith reference to certain embodiments thereof, other embodiments arepossible. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the embodiments contained herein.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncovers modifications and variations of this invention provided they fallwithin the scope of the following claims.

What is claimed is:
 1. An organic thin film transistor, comprising: asubstrate; a source/drain layer located on the substrate, and having asource region and a drain region; a first buffer layer located betweenthe source region and the drain region, and covering at least oneportion of the source region and at least one portion of the drainregion, wherein a top surface of the first buffer layer is not lowerthan a top surface of the source region and a top surface of the drainregion; a semiconductor layer located on the source/drain layer and thefirst buffer layer, wherein the first buffer layer is located among thesemiconductor layer, the source region, the drain region, and thesubstrate; a protective layer disposed along the semiconductor layer,wherein the semiconductor layer is located between the protective layerand the source/drain layer, and is located between the protective layerand the first buffer layer; a gate insulating layer covering thesource/drain layer and the semiconductor layer; a photoresist layerlocated on the protective layer and between the gate insulating layerand the protective layer; and a gate electrode located on the gateinsulating layer, wherein a portion of the gate insulating layer islocated between the gate electrode and the semiconductor layer.
 2. Theorganic thin film transistor of claim 1, further comprising: a barrierlayer located on the substrate, wherein the first buffer layer islocated among the semiconductor layer, the source region, the drainregion, and the barrier layer.
 3. The organic thin film transistor ofclaim 2, further comprising: a second buffer layer located on thebarrier layer, wherein the first buffer layer is located among thesemiconductor layer, the source region, the drain region, and the secondbuffer layer.
 4. The organic thin film transistor of claim 1, whereinthe source region has a bottom surface and the top surface opposite thebottom surface, and has a sidewall adjacent to the bottom surface andthe top surface, and the bottom surface faces the substrate, and anobtuse angle is formed between the sidewall and the bottom surface. 5.The organic thin film transistor of claim 4, wherein the first bufferlayer has a central portion and an extending portion, and the centralportion is located between the source region and the drain region, andthe extending portion is located on the top surface of the sourceregion.
 6. The organic thin film transistor of claim 5, wherein at leastone portion of the source region is located between the extendingportion and the central portion.
 7. The organic thin film transistor ofclaim 4, wherein the first buffer layer is in contact with the sidewallof the source region.
 8. The organic thin film transistor of claim 1,wherein the drain region has a bottom surface and a top surface oppositethe bottom surface, and has a sidewall adjacent to the bottom surfaceand the top surface, and the bottom surface faces the substrate, and anobtuse angle is formed between the sidewall and the bottom surface. 9.An organic thin film transistor, comprising: a substrate; a source/drainlayer located on the substrate, and having a source region and a drainregion; a first buffer layer located between the source region and thedrain region, and covering at least one portion of the source region andat least one portion of the drain region, wherein a top surface of thefirst buffer layer is not lower than a top surface of the source regionand a top surface of the drain region; a semiconductor layer located onthe source/drain layer and the first buffer layer, wherein the firstbuffer layer is located among the semiconductor layer, the sourceregion, the drain region, and the substrate; a barrier layer located onthe substrate, wherein the first buffer layer is located among thesemiconductor layer, the source region, the drain region, and thebarrier layer; a second buffer layer located on the barrier layer,wherein the first buffer layer is located among the semiconductor layer,the source region, the drain region, and the second buffer layer; a gateinsulating layer covering the source/drain layer and the semiconductorlayer; and a gate electrode located on the gate insulating layer,wherein a portion of the gate insulating layer is located between thegate electrode and the semiconductor layer.
 10. The organic thin filmtransistor of claim 9, wherein the source region has a bottom surfaceand the top surface opposite the bottom surface, and has a sidewalladjacent to the bottom surface and the top surface, and the bottomsurface faces the substrate, and an obtuse angle is formed between thesidewall and the bottom surface.
 11. The organic thin film transistor ofclaim 10, wherein the first buffer layer has a central portion and anextending portion, and the central portion is located between the sourceregion and the drain region, and the extending portion is located on thetop surface of the source region.
 12. The organic thin film transistorof claim 11, wherein at least one portion of the source region islocated between the extending portion and the central portion.
 13. Theorganic thin film transistor of claim 10, wherein the first buffer layeris in contact with the sidewall of the source region.
 14. The organicthin film transistor of claim 9, wherein the drain region has a bottomsurface and a top surface opposite the bottom surface, and has asidewall adjacent to the bottom surface and the top surface, and thebottom surface faces the substrate, and an obtuse angle is formedbetween the sidewall and the bottom surface.